Rehydration of micronized tecovirmimat monohydrate

ABSTRACT

Disclosed are methods for hydration of ST-246 particles comprising exposing said particles to moisture by conveying volumes of air containing moisture.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/906,119, filed on Nov. 19, 2013, the disclosure ofwhich is hereby fully incorporated herein by reference.

FIELD OF THE INVENTION

Described herein are methods for the preparation of stable micronizedmonohydrate form of Tecovirimat and its use for the treatment orprophylaxis of viral infections and diseases associated therewith,particularly those viral infections and associated diseases caused bythe orthopoxvirus. Tecovirimat, with a proprietary name of ST-246®, hasa chemical name ofN-[(3aR,4R,4aR,5aS,6S,6aS)-3,3a,4,4a,5,5a,6,6a-octahydro-1,3-dioxo-4,6-ethenocycloprop[f]isoindol-2(1H)-yl]-4-(trifluoromethyl)-benzamide.

BACKGROUND OF THE INVENTION

The Orthopox genus (Orthopoxviridae) is a member of the Poxviridaefamily and the Choropoxivirinae subfamily. The genus consists ofnumerous viruses that cause significant disease in human and animalpopulations. Viruses in the orthopox genus include cowpox, monkeypox,vaccinia, and variola (smallpox), all of which can infect humans.

The smallpox (variola) virus is of particular importance. Recentconcerns over the use of smallpox virus as a biological weapon haveunderscored the necessity of developing small molecule therapeutics thattarget orthopoxviruses. Variola virus is highly transmissible and causessevere disease in humans resulting in high mortality rates (Henderson etal. (1999) JAMA. 281:2127-2137). Moreover, there is precedent for use ofvariola virus as a biological weapon. During the French and Indian wars(1754-1765), British soldiers distributed blankets used by smallpoxpatients to American Indians in order to establish epidemics (Stern, E.W. and Stern, A. E. 1945. The effect of smallpox on the destiny of theAmerindian. Boston). The resulting outbreaks caused 50% mortality insome Indian tribes (Stern, E. W. and Stern, A. E.). More recently, theSoviet government launched a program to produce highly virulentweaponized forms of variola in aerosolized suspensions (Henderson,supra). Of more concern is the observation that recombinant forms ofpoxvirus have been developed that have the potential of causing diseasein vaccinated animals (Jackson et al. (2001) J. Virol., 75:1205-1210).

The smallpox vaccine program was terminated in 1972; thus, manyindividuals are no longer immune to smallpox infection. Even vaccinatedindividuals may no longer be fully protected, especially against highlyvirulent or recombinant strains of virus (Downie and McCarthy. (1958) JHyg. 56:479-487; Jackson, supra). Therefore, mortality rates would behigh if variola virus were reintroduced into the human population eitherdeliberately or accidentally.

Variola virus is naturally transmitted via aerosolized droplets to therespiratory mucosa where replication in lymph tissue producesasymptomatic infection that lasts 1-3 days. Virus is disseminatedthrough the lymph to the skin where replication in the small dermalblood vessels and subsequent infection and lysis of adjacent epidermalcells produces skin lesions (Moss, B. (1990) Poxviridae and TheirReplication, 2079-2111. In B. N. Fields and D. M. Knipe (eds.), FieldsVirology. Raven Press, Ltd., New York). Two forms of disease areassociated with variola virus infection; variola major, the most commonform of disease, which produces a 30% mortality rate and variola minor,which is less prevalent and rarely leads to death (<1%). Mortality isthe result of disseminated intravascular coagulation, hypotension, andcardiovascular collapse, which can be exacerbated by clotting defects inthe rare hemorrhagic type of smallpox (Moss, supra).

A recent outbreak of monkeypox virus underscores the need for developingsmall molecule therapeutics that target viruses in the orthopox genus.Appearance of monkeypox in the US represents an emerging infection.Monkeypox and smallpox cause similar diseases in humans, howevermortality for monkeypox is lower (1%).

Vaccination is the current means for preventing orthopox virus disease,particularly smallpox disease. The smallpox vaccine was developed usingattenuated strains of vaccinia virus that replicate locally and provideprotective immunity against variola virus in greater than 95% ofvaccinated individuals (Modlin (2001) MMWR (Morb Mort Wkly Rep)50:1-25). Adverse advents associated with vaccination occur frequently(1:5000) and include generalized vaccinia and inadvertent transfer ofvaccinia from the vaccination site. More serious complications such asencephalitis occur at a rate of 1:300,000, which are often fatal(Modlin, supra). The risk of adverse events is even more pronounced inimmunocompromised individuals (Engler et al. (2002) J Allergy ClinImmunol. 110:357-365). Thus, vaccination is contraindicated for peoplewith AIDS or allergic skin diseases (Engler et al.). While protectiveimmunity lasts for many years, the antibody response to smallpoxvaccination is significantly reduced 10 to 15 years post inoculation(Downie, supra). In addition, vaccination may not be protective againstrecombinant forms of orthopoxvirus. A recent study showed thatrecombinant forms of mousepox virus that express IL-4 cause death invaccinated mice (Jackson, supra). Given the side effects associated withvaccination, contraindication of immunocompromised individuals, andinability to protect against recombinant strains of virus, betterpreventatives and/or new therapeutics for treatment of smallpox virusinfection are needed.

Vaccinia virus immunoglobulin (VIG) has been used for the treatment ofpost-vaccination complications. VIG is an isotonic sterile solution ofimmunoglobulin fraction of plasma derived from individuals who receivedthe vaccinia virus vaccine. It is used to treat eczema vaccinatum andsome forms of progressive vaccinia. Since this product is available inlimited quantities and difficult to obtain, it has not been indicatedfor use in the event of a generalized smallpox outbreak (Modlin, supra).

Cidofovir ([(S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine][HBMPC]) is a nucleoside analog approved for treatment of CMV retinitisin AIDS patients. Cidofovir has been shown to have activity in vitroagainst a number of DNA containing viruses including adenovirus,herpesviruses, hepadnaviruses, polyomaviruses, papillomaviruses, andorthopoxviruses (Bronson et al. (1990) Adv. Exp. Med. Biol. 278:277-83;De Clercq et al. (1987) Antiviral Res. 8:261-272; de Oliveira et al.(1996) Antiviral Res. 31:165-172; Snoeck et al. (2001) Clin Infect. Dis.33:597-602). Cidofovir has also been found to inhibit authentic variolavirus replication (Smee et al. (2002) Antimicrob. Agents Chemother.46:1329-1335).

However, cidofovir administration is associated with a number of issues.Cidofovir is poorly bioavailable and must be administered intravenously(Laezari et al. (1997) Ann. Intern. Med. 126:257-263). Moreover,cidofovir produces dose-limiting nephrotoxicity upon intravenousadministration (Lalezari et al.). In addition, cidofovir-resistance hasbeen noted for multiple viruses. Cidofovir-resistant cowpox, monkeypox,vaccinia, and camelpox virus variants have been isolated in thelaboratory by repeated passage in the presence of drug (Smee, supra).Cidofovir-resistance represents a significant limitation for use of thiscompound to treat orthopoxvirus replication. Thus, the poorbioavailability, need for intravenous administration, and prevalence ofresistant virus underscores the need for development of additional andalternative therapies to treat orthopoxvirus infection.

In addition to viral polymerase inhibitors such as cidofovir, a numberof other compounds have been reported to inhibit orthopoxvirusreplication (De Clercq. (2001) Clin Microbiol. Rev. 14:382-397).Historically, methisazone, the prototypical thiosemicarbazone, has beenused in the prophylactic treatment of smallpox infections (Bauer et al.(1969) Am. J Epidemiol. 90:130-145). However, this compound class hasnot garnered much attention since the eradication of smallpox due togenerally unacceptable side effects such as severe nausea and vomiting.Mechanism of action studies suggest that methisazone interferes withtranslation of L genes (De Clercq (2001), supra). Like cidofovir,methisazone is a relatively non-specific antiviral compound and caninhibit a number of other viruses including adenoviruses,picornaviruses, reoviruses, arboviruses, and myxoviruses (Id.).

Another class of compounds potentially useful for the treatment ofpoxviruses is represented by inhibitors of S-adenosylhomocysteinehydrolase (SAH). This enzyme is responsible for the conversion ofS-adenosylhomocysteine to adenosine and homocysteine, a necessary stepin the methylation and maturation of viral mRNA. Inhibitors of thisenzyme have shown efficacy at inhibiting vaccinia virus in vitro and invivo (De Clercq et al. (1998) Nucleosides Nucleotides. 17:625-634.).Structurally, all active inhibitors reported to date are analogues ofthe nucleoside adenosine. Many are carbocyclic derivatives, exemplifiedby Neplanacin A and 3-Deazaneplanacin A. While these compounds haveshown some efficacy in animal models, like many nucleoside analogues,they suffer from general toxicity and/or poor pharmacokinetic properties(Coulombe et al. (1995) Eur. J Drug Metab Pharmacokinet. 20:197-202;Obara et al. (1996) J Med. Chem. 39:3847-3852). It is unlikely thatthese compounds can be administered orally, and it is currently unclearwhether they can act prophylactically against smallpox infections.Identification of non-nucleoside inhibitors of SAH hydrolase, and otherchemically tractable variola virus genome targets that are orallybioavailable and possess desirable pharmacokinetic (PK) and absorption,distribution, metabolism, excretion (ADME) properties would be asignificant improvement over the reported nucleoside analogues. Insummary, currently available compounds that inhibit smallpox virusreplication are generally non-specific and suffer from use limitingtoxicities and/or questionable efficacies.

In U.S. Pat. No. 6,433,016 (Aug. 13, 2002) and U.S. ApplicationPublication 2002/0193443 A1 (published Dec. 19, 2002) a series ofimidodisulfamide derivatives are described as being useful fororthopoxvirus infections.

New therapies and preventatives are clearly needed for infections anddiseases caused by orthopoxvirus infection.

The co-owned PCT publication WO 2004/112718 (published Dec. 29, 2004)discloses the use of di, tri, and tetracyclic acylhydrazide derivativesand analogs, as well as pharmaceutical compositions containing the same,for the treatment or prophylaxis of viral infections and diseasesassociated therewith, particularly those viral infections and associateddiseases caused by the orthopoxvirus. The co-owned U.S. Patentpublication 2008/0004452 (published Jan. 3, 2008) further discloses aprocess for producing ST-246.

Finally, the co-owned PCT publication WO 2011/119698 described thatST-246 can exist in multiple different polymorphic forms. A particularcrystalline form of a compound may have physical properties that differfrom those of other polymorphic forms and such properties may influencemarkedly the pharmaceutical processing of the compound and theperformance of the resulting dosage form, particularly when the compoundis prepared or used on a commercial scale. Such differences may alterthe mechanical handling properties of the compound (such as the flowcharacteristics of the solid material) and the compressioncharacteristics of the compound. Further, the discovery of newpolymorphic forms of such pharmaceutically important compound as ST-246,provided a new opportunity to improve the performance characteristics ofa pharmaceutical end product and enlarged the repertoire of materialsthat a formulation scientist has available for designing, for example, apharmaceutical dosage form of a drug with targeted release profile orother desired physical-chemical properties, such as stability.

New polymorphic forms of a drug substance may display different meltingpoint, hygroscopicity, stability, solubility and/or dissolution rate,crystallinity, crystal properties, bioavailability, toxicity andformulation handling characteristics, which are among the numerousproperties that need to be considered in preparing a medicament that canbe effectively administered. Furthermore, regulatory agencies requiredefinitive knowledge, characterization and control of the polymorphicform of the active component in solid pharmaceutical dosage forms.Tecovirimat has low solubility in aqueous solutions and hence forefficient oral absorption and efficacy, the drug needs to be micronizedto get very fine particles. Fine particle size is usually achieved bymilling or micronization. Particle size reduction of tecovirimatmonohydrate, however, exhibits dehydration upon micronization. In viewof the foregoing, there is a need to have a process that product stablemicronized monohydrate. Thus, a rehydration process was developedaccording to the present invention as described below.

SUMMARY OF THE INVENTION

The present invention provides a method of hydrating ST-246 particlescomprising exposing said particles to moisture by conveying volumes ofair containing moisture to said particles.

The present invention also provides for reducing the particle size ofST-246 particles comprising:

(a) micronizing ST-246 micronized using an air jet mill in order toreduce particle size to (D90<10 microns) resulting in ST-246 particlesthat are dehydrated to some extent relative to the ST-246 particlesprior to micronization; and

(b) rehydrating said micronized ST-246 particles by exposing saiddehydrated particles to moisture by conveying volumes of air containingmoisture to said dehydrated particles.

The present invention further provides a method of converting ST-246polymorph particles exhibiting dehydration to ST-246 polymorph Form Imonohydrate particles comprising exposing said partially dehydratedST-246 polymorph particles to moisture by conveying volumes of aircontaining moisture to said particles. ST-246 monohydrate polymorph FormI is desirable for its pharmaceutical properties such as stability, lackof hygroscopicity, and processability.

DETAILED DESCRIPTION OF THE INVENTION

Described herein are processes for producing ST-246. The chemical namefor ST-246 isN-[(3aR,4R,4aR,5aS,6S,6aS)-3,3a,4,4a,5,5a,6,6a-octahydro-1,3-dioxo-4,6-ethenocycloprop[f]isoindol-2(1H)-yl]-4-(trifluoromethyl)-benzamideand has the following formula:

Definitions

In accordance with this detailed description, the followingabbreviations and definitions apply. It must be noted that as usedherein, the singular forms “a,” “an,” and “the” include plural referentsunless the context clearly dictates otherwise.

The term “polymorphic form, polymorph, polymorph form, crystalline form,physical form or crystalline polymorph” of ST-246 in the presentinvention refers to a crystal modification of ST-246, which can becharacterized by analytical methods such as X-ray powder diffractionpattern (XRPD), differential scanning calorimetry (DSC), by its meltingpoint analysis, or Infrared Spectroscopy (FTIR), or polarized lightmicroscopy.

The term “hydrate” as used herein means a compound or a salt thereofthat further includes a stoichiometric or non-stoichiometric amount ofwater bound by non-covalent intermolecular forces. The term monohydrateas used herein refers to crystal forms formed by the combination of onemolecule of water with one molecule of the substance in which the waterretains its molecular state as H₂O, such combinations being able to formone or more hydrate polymorph. The term “hemihydrate” as used hereinrefers to a solid with 0.5 molecule of H₂O per molecule of thesubstance.

The term “pharmaceutical composition” or “pharmaceutical formulation” isintended to encompass a drug product including the active ingredient(s),pharmaceutically acceptable excipients that make up the carrier, as wellas any product which results, directly or indirectly, from combination,complexation or aggregation of any two or more of the ingredients.Accordingly, the pharmaceutical compositions of the present inventionencompass any composition made by admixing the active ingredient, activeingredient dispersion or composite, additional active ingredient(s), andpharmaceutically acceptable excipients.

PCT publication WO 2011/119698 discloses 6 polymorphs or crystalstructures for ST-246 with various degrees of hydration. Form I ofST-246 is a monohydrate form that shows an X-ray powder diffractionpattern having characteristic peaks of about7.63,10.04,11.47,14.73,15.21,15.47,16.06,16.67,16.98,18.93,19.96,20.52,20.79,22.80,25.16,26.53,27.20,27.60,29.60,30.23,30.49,30.68,31.14,33.65,34.33,35.29,35.56,36.30,37.36,38.42,38.66degrees.

Polymorphs Forms II and IV are anhydrate crystalline forms of ST-246.Anhydrate Form IV is relatively unstable when exposed to ambientconditions and prone to conversion to Form V, due to absorption ofmoisture.

Form V is a hemihydrate crystalline form of ST-246. Examples of XRPDdata for Form V are shown below:

Angle d value Intensity 2-Theta ° Angstrom Cps Intensity % 6.39 13.81101 100.0 6.72 13.14 9.56 9.5 8.16 10.82 1.88 1.9 9.04 9.78 3.75 3.79.52 9.28 6.38 6.3 10.52 8.41 4.88 2.1 12.40 7.13 5.06 5.0 12.79 6.927.31 7.3 13.38 6.61 4.13 4.1 14.15 6.25 12.0 11.9 14.57 6.07 11.4 11.415.84 5.59 15.9 15.9 16.32 5.43 10.7 10.6 16.67 5.31 25.7 25.6 17.505.06 21.2 21.1 18.13 4.89 9.19 9.1 18.48 4.80 5.44 5.4 18.78 4.72 16.916.8 19.79 4.48 38.3 38.1 20.68 4.29 17.3 17.2 21.07 4.21 13.9 13.821.54 4.12 5.25 5.2 22.01 4.04 5.81 5.8 22.73 3.91 7.50 7.5 23.60 3.776.38 6.3 25.25 3.52 4.50 4.5 25.73 3.46 20.1 20.0 26.27 3.39 3.94 3.926.73 3.33 5.63 5.6 27.24 3.27 13.3 13.2 29.02 3.07 10.1 10.1 29.50 3.038.06 8.0 29.83 2.99 6.94 6.9 30.44 2.93 9.00 9.0 32.04 2.79 4.50 4.533.52 2.67 7.13 7.1 34.84 2.57 4.69 4.7 35.68 2.51 6.19 6.2 39.78 2.264.31 4.3

It has been reported that air jet milling of hydrates of organiccompounds to reduce particle size can lead to dehydration (Kang,F.,Cryst. Growth Des. 2012, 12, 60-74; and Ito, S. J. Pharm. Sci, 1996,85, 1117-1122). Dehydration may be directly caused by exposure of thedrug substance to the very dry compressed air used for air jet milling.In addition, reduction in particle size may allow moisture to be removedfrom the crystal more readily. Air-jet milling is generally consideredto involve the least mechanical/thermal stress to the API compared toother techniques, and other techniques are unlikely to be suitable forparticle size reduction to less than 10 microns. SIGA discovered thatST-246 Form I monohydrate can become dehydrated as a result of air jetmilling, based on precise determinations of water content.

The ST-246 drug substance manufacturing process consistently producesST-246 monohydrate (polymorph Form I). ST-246 monohydrate is micronizedusing an air jet mill in order to reduce particle size (D90<10 microns)as required for acceptable bioavailability. After scale-up of themicronization process to commercial scale, the micronized Form I wasfound to partially convert to hemihydrate polymorph Form V upon storageunder certain conditions. The root cause was determined to bedehydration of the monohydrate Form I during micronization. When storedwith limited exposure to ambient air, the dehydrated material canconvert to the hemi-hydrate Form V. This was unexpected, as ST-246monohydrate is nonhygroscopic over the relative humidity (RH) range of10-90% and only undergoes dehydration at very low RH (<3-6% RH). In thepresent invention, methods to re-introduce moisture into the dehydratedST-246 molecule are disclosed in order to rapidly obtain the desiredmonohydrate moisture level, thereby preventing conversion to Form V uponstorage.

Surprisingly, dehydrated micronized ST-246 monohydrate rapidly absorbsmoisture, so rehydration is feasible at humidity levels present inambient air. Rehydration of partially dehydrated ST-246 to themonohydrate level has been successfully demonstrated on a commercialscale as indicated in the examples below. Preferably, rehydration can becarried out using a technique selected from: Turboscreen; High ShearGranulator; Tray Drying; Vibratory sifter/sieve; Mixer/blender; andFluid bed dryer. This technique can be used for other substances thatundergo dehydration upon micronization.

Accordingly, the present invention provides a method of hydrating ST-246particles comprising exposing said particles to moisture by conveyingvolumes of air containing moisture to said particles. Preferably, thehydrated ST-246 is micronized ST-246 polymorph monohydrate (PolymorphForm I). Preferably, the exposure of ST-246 particles to moisture takesplace during a process selected from the group consisting of:Turboscreen, High Shear Granulator, Tray Drying, Vibratory sifter/sieve,Mixer/blender, and Fluid bed dryer, more preferably High ShearGranulator, most preferably Turboscreen.

The present invention also provides a method for reducing the particlesize of ST-246 particles comprising:(a) micronizing ST-246 using an airjet mill in order to reduce particle size to (D90<10 microns) resultingin partially dehydrated ST-246 particles relative the ST-246 particlesprior to micronization; and (b) rehydrating said micronized ST-246particles by exposing said dehydrated particles to moisture by conveyingvolumes of air containing moisture to said dehydrated particles.Preferably, the ST-246 prior to micronization is ST-246 monohydrate(Polymorph Form I). Preferably, the micronization step is carried out ata humidity of less than about 60% RH, more preferably less than about40% RH).

The present invention also provides for a method of converting ST-246polymorph particles to ST-246 polymorph monohydrate particles comprisingexposing said ST-246 polymorph particles to moisture by conveyingvolumes of air containing moisture to said particles. Preferably, themethods of the present invention further prevent the conversion ofST-246 polymorph particles to ST-246 polymorph hemihydrate particles(ST-246 Polymorph Form V).

The benefit of the rehydration is improved solid-form stability, andtherefore shelf-life, of micronized ST-246 monohydrate. Without therehydration process, it would not be possible to consistently producemicronized ST-246 monohydrate at commercial scale, without partialconversion to Form V during storage. The equipment described in thisinvention is common and readily available, and can easily be used torehydrate ST-246 without modification. The TurboScreen process ishigh-yielding. After five passes through the equipment, only 3-4% ofmaterial is lost. No significant change in particle size distributionhas been observed after the TurboScreen process.

More details about the Turboscreen, High Shear Granulator, and TrayDrying processes are provided below.

Vibratory Sifter/Sieve:

Typical applications include sifting, scalping, classifying, de-dustingand de-lumping of dry bulk solids. Vibration causes particles to passthrough a screen. When done in an atmosphere of humidified air, thisallows exposure of product to moisture.

Mixer/Blender:

Several blender types (including tumble and ribbon) could be used forrehydration according to the present invention. Blender movements(rotation or inversion) increase the mobility of the individualparticles and thus promote diffusive blending. Diffusion blending occurswhere the particles are distributed over a freshly developed interface.Since the blender is rotating, the air/bed interface is constantlyrenewing. In the absence of segregating effects, the diffusive blendingwill in time lead to a high degree of homogeneity. V-Blenders aretherefore preferred when precise blend formulations are required. Theyare also well suited for applications where some ingredients may be aslow as one percent of the total blend size. A V-blender could bemodified to humidify API if the intensifier bar were replaced with aperforated tube for humid air injection during tumbling. However, amethod of venting the blender would need to be devised such thatmaterial would not be lost when the vent points down.

Fluid Bed Dryer:

Fluid bed dryers could be used for rehydration according to the presentinvention. This would be an efficient method, due to fluidization ofsolid material in a large volume of air.

Rehydration of Micronized Product: Since dehydration was concluded to bethe driver for formation of hemihydrate Form V upon storage ofmicronized ST-246 monohydrate, a rehydration process has been developedto increase the moisture level of the partially dehydrated material tothe monohydrate moisture level. DVS studies indicated that dehydratedST-246 monohydrate rapidly absorbs moisture, so rehydration is feasibleat humidity levels present in ambient air. The rehydration processutilizes a Sweco Turbo-Screen. The Turbo-Screen uses large volumes ofroom air to convey the product through a screen, and is therefore anefficient way to expose the product to moisture. The screen pore size isselected such that no particle size discrimination of the ST 246 API isexpected. To ensure a consistent, robust rehydration process, therelative humidity in the processing suite will be controlled at 40 60%RH.

Turbo-Screen rehydration feasibility studies have been performed, andare discussed below. These studies were conducted using micronizedmaterial

Commercial scale unmicronized ST-246 monohydrate (commercial validationbatch SG 10A11 Q) was micronized using a commercial scale 30″ mill andprocessed through a pilot scale Turbo-Screen. The effect of multiplepasses (up to 5) of material through the Turbo-Screen was evaluated.Data from the trial are summarized in Table-1. The Turbo-Screen processwas found to effectively increase moisture content from 4.04.5%.Material collected before and after the Turbo-Screen process wasplaced on an informal accelerated stability study, in sealed aluminumpouches staged at 37 40° C. and 50° C.XRPD results from this study todate are summarized in Table-2.

TABLE 1 Summary of Turbo-Screen Feasibility Study 5665/5677 Trial 5677Trial 5665 Turbo-Screen Test Freshly Micronized (5 Passes) Particle Size(D90; microns) 4.0 4.0 Moisture Content (KF) 4.0% 4.5%

TABLE 2 Informal Stability Study on Turbo-Screen Feasibility Study5665/5677 (XRPD Results) Storage Trial 5665 - Trial 5677 Condition/TimeFreshly Micronized Turbo-Screen (5 Passes) 37-40° C. 11 days Form Vpresent^(a) Not Tested 1 month Form V present Conforms to Form I, Form Vnot detected 6 months Not Tested Conforms to Form I, Form V not detected50° C. 2 weeks Not Tested Conforms to Form I, Form V not detected^(a)Form V in sample shown by presence of reflections in XRPDdiffractogram at ~6.3 and 14.1 degrees 2-theta.

Stability Studies: After 6 months at 37 40° C., and 2 weeks at 50° C.,the material rehydrated via Turbo-Screen has not shown the presence ofhemihydrate Form V. The freshly micronized material showed Form V afterjust 11 days at 37 40° C. The particle size of this material was smallerthan product typically produced in the commercial scale mill (D90 of ˜4microns rather than˜6 microns) due to the lower feed rate used duringthis trial (˜50 kg/hr rather than 100 kg/hr during typical processing).

Turbo-Screen Optimization Study—Study 5707: Material micronized wasprocessed through a commercial scale Turbo-Screen for up to five passes.Results are summarized in Table 3. During these trials, the humidity inthe processing suite was increased using a portable room humidifier andranged from approximatly 28 58% RH. Powdersize is upgrading its HVACsystem to control humidity of the processing suite at 40 60% RH, andthis system will be qualified prior to validation of the rehydrationprocess.

TABLE 3 Summary of Micronization and Turbo- Screen Optimization Study5707 Particle Mill Feed Moisture Moisture Size Pressure Rate Content %Content % (D90; Trial (psi) (kg/hr) (SIGA) (Powdersize) microns) Trial1 - 115 100  4.3 4.4 7.6 Freshly Micronized (FM) Trial 1 - Turbo-ScreenFeed 4.5 4.5 7.6 Turbo- Rate: 100 kg/hr Screen Pass 1 (TS-1) TS-2 4.64.6 7.6 TS-3 4.6 4.5 7.3 TS-4 4.6 4.5 8.3 TS-5 4.6 4.6 7.8 Trial 2-FM115 160  4.3 4.3 8.7 TS-1 Turbo-Screen Feed Not 4.5 8.4 Rate: 100 kg/hrTested TS-2 4.6 4.6 8.7 TS-3 4.7 4.5 8.5 Trial 4-FM 105 60 4.0 4.2 6.2TS-1 Turbo-Screen Feed 4.5 4.4 5.9 TS-2 Rate: 100 kg/hr 4.6 4.5 6.7 TS-34.5 4.6 7.0 TS-4 4.6 4.5 6.3 TS-5 4.7 4.5 6.5 Trial 5-FM 115 75 4.2 4.26.7 TS-1 Turbo-Screen Feed 4.6 4.5 7.3 TS-2 Rate: 100 kg/hr 4.6 4.6 7.2TS-3 4.7 4.6 7.6 TS-4 4.7 4.5 7.4 TS-5 4.7 4.6 7.1 Trial 6-FM 115 75 4.14.1 6.5 TS-1 Turbo-Screen Feed 4.5 4.5 6.3 TS-2 Rate: 200 kg/hr 4.6 4.56.8 TS-3 4.6 4.5 6.7 TS-4 4.6 4.6 6.7 TS-5 4.6 4.6 6.7

These results show that the Turbo-Screen process can successfullyrehydrate the micronized material to a level consistent with themonohydrate (theoretical value of 4.57%). The Turbo Screen rehydrationprocess does not cause any significant change to particle size of theproduct.

EXAMPLE 1 ST-246 Rehydration Using Turboscreen

Turboscreening is typically used to remove a small fraction of oversizedparticles from large quantities of a bulk material. The Turbo-Screenuses large volumes of atmosphere air to convey the product through ascreen, and is therefore an efficient way to expose the product tomoisture. The screen pore size is selected to minimize particle sizediscrimination of ST-246. To ensure a consistent, robust rehydrationprocess, the relative humidity in the processing suite is controlledat >30%% RH. Material that has been passed through the Turboscreenequipment either 3, 4, or 5 passes has shown a good stability profile,as evidenced by lack of formation of hemihydrate Form V.

Micronized API particles freely mix with the rapidly moving humidifiedair before encountering a tensile bolt cloth mesh screen that breaks uplumps; further exposing the API to moist air. The humidified micronizedmaterial is then separated from the airstream in a cyclone anddischarged to drums. Multiple separate passes were employed through theTurboscreen to ensure that the micronized API has been rehydrated to themonohydrate moisture level. Screens are continually swept with arotating wand utilizing high pressure air to clean the screen andmaintain high throughput. These are commercially feasible processes withno change in the physical properties of the particles such as particlesize distribution, bulk and tap densities. Experimental Procedure: Theequipment used for micronization and hydration are the following: A 30″OD/24″ ID Spiral pancake Jet Mill equipped with a Volumetric SingleScrew Auger Feeder w/60mm flights and a 30″ Sweco Turbo-Screenrespectively Unmicronized ST-246 was micronized at a Feed rate of 60 to200 kg/hour and a mill pressure of 95 to 115 psi. The particle size ismonitored during the micronization process using dynamic laser lightmeasurements. The feed rate and the mill pressure was optimized to giveproduct with optimal particle size. Rehydration was done using theTurbo-screen with feed rates up to approximately 200 kg/hr. Howeverlower feed rates could provide more efficient rehydration, due to betterexposure to air inside the equipment. Materials have been Turbo-Screenedby passing through the Turbo screen with more than 1 passes. Thesematerials have shown good chemical and polymorphic stability profile.Rehydration has been successful with processing suite humidity levels aslow as 30% to 60% RH. Tecovirimat monohydrate does not continue toabsorb moisture once fully hydrated, so there is no risk ofover-hydration.

EXAMPLE 2 ST-246 Rehydration Using High Shear Granulator

High shear granulation is typically used to agglomerate small particlestogether by the addition of a binder solution to a stirred vessel ofparticles and powders with blades driven by powerful motors. The bottomblade, the plow, turns slowly to force moistened particles into intimatecontact with each other while driving out air. The smaller verticalchopper blade spins rapidly to break up lumps that form. To use forhumidification, the blades would both be spinning rapidly to keep theparticle bed fluffed up while moist air was forced into thebowl—preferably near the bottom of the bed and through multiple inlets.A filter at the top of the unit prevents particle escape while allowingfor air passage.

Experimental Procedure: A 3 to 5 kg batch of micronized ST-246 drugsubstance (form I) is charged into a High Shear Granulator VG 25. Thegranulator lid is closed while keeping open the exhaust filter port andthe Inspection window. The ST-246 is hydrated using an external sourceof moist air with mixing in the VG 25 and with the blade speed set to 25rpm and, cork screw at 0 rpm i.e power off for a period of severalhours. The moisture content of the ST-246 was determined using the Karlfisher method for moisture determination. The theoretical moisturecontent for ST-246 monohydrate is 4.54% w/w.

The ST-246 drug substance that underwent hydration using the aboveprocess was analyzed for moisture content, particle size, andpolymorphic stability studies using XRPD. The results are summarizedbelow:

Moisture PSD (D90, D50 and Sample content (% w/w) D10 in microns) Beforegranulator 4.17 4.1, 1.8, 1.2 humidification After granulator 4.48, 4.524.2, 2.4, 1.4 humidification XRPD of Humidified Conforms to Form I,showed sample stored 1 no polymorphic Form V. wk at 50° C.

These results indicate that:

-   -   1. Freshly micronized ST-246 can be hydrated to its monohydrate        state using High shear granulator, with no changes in the        particle size distribution.    -   2. Accelerated stability studies (at 50° C.) showed the        polymorphic stability of Form I and absence of formation of Form        V.

EXAMPLE3 ST-246 Rehydration Using Tray Drying

Tray drying is typically used to dry a product. However, the cabinetequipment could be modified to provide a moist environment rather than adry one. As the name implies, material is spread over open trays andexposed to the atmosphere. In the pharmaceutical industry, theatmosphere is usually controlled for both temperature and relativehumidity and includes fans to evenly expose the trays. Depth of theproduct in the trays determines whether thehumidification/dehumidification is even through the product. Traysystems have been devised that are continuous in operation such that thematerial would be much more homogeneous in moisture content uponexiting.

Experimental Procedure: 1) Thirty grams of partially dehydratedmicronized ST-246 was spread in a tray and placed on a benchtop underambient temperature and a humidity of 20-30%, 2) one gram of partiallydehydrated micronized ST-246 was spread in a tray and placed on Astability chamber with controlled temperature and humidity at 25° C./60%RH and 3) one gram of partially dehydrated micronized ST-246 was spreadin a tray and placed on a stability chamber with controlled temperatureand humidity at 40° C./75% RH. After 18 hours at bench top or 2 hours at25° C./60% RH or 2 hours at 40° C./75% RH, the moisture content ofST-246 was determined using Karl Fisher method for moisturedetermination. These results showed that ST-246 API was re-hydrated tomoisture levels at ˜4.5% and confirmed by XRPD data to be Form I.Furthermore, the humidified API demonstrated polymorphic stability whenpackaged in sealed aluminum bag and staged at 37° C. for 3 months. Theseresults suggest that freshly micronized ST-246 can be rehydrated byexposing to atmosphere at different humidity level and the rehydratedST-246 shows polymorphic stability.The results are summarized below.

Moisture (% w/w Sample KF) XRPD DSC (° C.) SEM Freshly NA Form I 129.7,195.9 No Change in Micronized particle Hydration and ~4.5% Form I:128.9, 196.7 morphology sealed aluminum Showed bag stored at no Form 37°C. for 3 V. months.

All references cited herein are herein incorporated by reference intheir entirety for all purposes.

The invention has been described in terms of preferred embodimentsthereof, but is more broadly applicable as will be understood by thoseskilled in the art. The scope of the invention is only limited by thefollowing claims.

What is claimed is:
 1. A method of hydrating ST-246 particles comprisingexposing said particles to moisture by conveying volumes of aircontaining moisture to said particles.
 2. The method of claim 1, whereinsaid hydrated ST-246 is ST-246 polymorph Form I monohydrate.
 3. Themethod of claim 1, wherein said ST-246 particles prior to hydration areST-246 polymorph hemihydrate or ST-246 polymorph anhydrate.
 4. Themethod of claim 1, wherein the exposure by ST-246 particles to moisturetakes place during a process selected from the group consisting of:Turboscreen, High Shear Granulator, Tray Drying, Vibratory sifter/sieve,Mixer/blender, and Fluid bed dryer.
 5. The method of claim 1, whereinthe exposure by ST-246 particles to moisture takes place duringturboscreening.
 6. The method of claim 1, wherein the exposure by ST-246particles to moisture takes place during high shear granulation.
 7. Amethod for reducing the particle size of ST-246 particles comprising:(a) micronizing ST-246 micronized using an air jet mill in order toreduce particle size to (D90<10 microns) resulting in ST-246 particlesexhibiting some extent of dehydration relative to the ST-246 particlesprior to micronization; and (b) rehydrating said micronized ST-246particles by exposing said partially dehydrated particles to moisture byconveying volumes of air containing moisture to said dehydratedparticles.
 8. The method of claim 7, wherein said ST-246 prior tomicronization is ST-246 monohydrate.
 9. The method of claim 7, whereinsaid dehydrated ST-246 particles are ST-246 polymorph hemihydrate. 10.The method of method of claim 7, wherein the exposure of ST-246particles to moisture takes place during a process selected from thegroup consisting of: Turboscreen, High Shear Granulator, Tray Drying,Vibratory sifter/sieve, Mixer/blender, and Fluid bed dryer.
 11. Themethod of claim 7, wherein the exposure by ST-246 particles to moisturetakes place during turboscreening.
 12. The method of claim 7, whereinthe exposure by ST-246 particles to moisture takes place during highshear granulation.
 13. The method of claim 7, further preventing theconversion of ST-246 partially dehydrated polymorph Form I micronizedparticlesparticles to ST-246 polymorph hemihydrate particles.